linux-kernel - [PATCH] x86 : revert replace LOCK

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Date:	Fri, 15 Aug 2008 12:45:09 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <srostedt@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Roland McGrath <roland@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <williams@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] x86 : revert replace LOCK_PREFIX in futex.h

Depends on :

x86 alternatives : fix LOCK_PREFIX race with preemptible kernel and CPU hotplug

On Thu, 14 Aug 2008, Mathieu Desnoyers wrote:
>
> Changing the 0x90 (single-byte nop) currently used into a 0x3E DS segment
> override prefix should fix this issue. Since the default of the atomic
> instructions is to use the DS segment anyway, it should not affect the
> behavior.

Ok, so I think this is an _excellent_ patch, but I'd like to also then use
LOCK_PREFIX in include/asm-x86/futex.h.

See commit 9d55b9923a1b7ea8193b8875c57ec940dc2ff027.

                Linus

Applies to 2.6.27-rc2 (and -rc3 unless hell broke loose in futex.h between rc2
and rc3).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: H. Peter Anvin <hpa@...or.com>
CC: Jeremy Fitzhardinge <jeremy@...p.org>
CC: Roland McGrath <roland@...hat.com>
CC: Ingo Molnar <mingo@...e.hu>
Cc: Steven Rostedt <rostedt@...dmis.org>
CC: Steven Rostedt <srostedt@...hat.com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: David Miller <davem@...emloft.net>
CC: Ulrich Drepper <drepper@...hat.com>
CC: Rusty Russell <rusty@...tcorp.com.au>
CC: Gregory Haskins <ghaskins@...ell.com>
CC: Arnaldo Carvalho de Melo <acme@...hat.com>
CC: "Luis Claudio R. Goncalves" <lclaudio@...g.org>
CC: Clark Williams <williams@...hat.com>
CC: Christoph Lameter <cl@...ux-foundation.org>
CC: Andi Kleen <andi@...stfloor.org>
CC: Harvey Harrison <harvey.harrison@...il.com>
---
 include/asm-x86/futex.h |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6-lttng/include/asm-x86/futex.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86/futex.h	2008-08-15 12:32:38.000000000 -0400
+++ linux-2.6-lttng/include/asm-x86/futex.h	2008-08-15 12:41:33.000000000 -0400
@@ -25,7 +25,7 @@
 	asm volatile("1:\tmovl	%2, %0\n"			\
 		     "\tmovl\t%0, %3\n"				\
 		     "\t" insn "\n"				\
-		     "2:\tlock; cmpxchgl %3, %2\n"		\
+		     "2:\t" LOCK_PREFIX "cmpxchgl %3, %2\n"	\
 		     "\tjnz\t1b\n"				\
 		     "3:\t.section .fixup,\"ax\"\n"		\
 		     "4:\tmov\t%5, %1\n"			\
@@ -64,7 +64,7 @@ static inline int futex_atomic_op_inuser
 		__futex_atomic_op1("xchgl %0, %2", ret, oldval, uaddr, oparg);
 		break;
 	case FUTEX_OP_ADD:
-		__futex_atomic_op1("lock; xaddl %0, %2", ret, oldval,
+		__futex_atomic_op1(LOCK_PREFIX "xaddl %0, %2", ret, oldval,
 				   uaddr, oparg);
 		break;
 	case FUTEX_OP_OR:
@@ -122,7 +122,7 @@ static inline int futex_atomic_cmpxchg_i
 	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
 		return -EFAULT;
 
-	asm volatile("1:\tlock; cmpxchgl %3, %1\n"
+	asm volatile("1:\t" LOCK_PREFIX "cmpxchgl %3, %1\n"
 		     "2:\t.section .fixup, \"ax\"\n"
 		     "3:\tmov     %2, %0\n"
 		     "\tjmp     2b\n"

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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